The present invention is directed to a method and system for controlling slave station activities in a communications network in which any number of master stations may independently assert control at any time, and more particularly to a supervisory system for a network of stations that communicate data, video and/or telephone signals using media in which any one of the communications stations may be used to monitor and/or control the activities at any other station.
A supervisory system for a network of communications stations typically uses a master station to control and monitor the status of the other stations (collectively referred to herein as slave stations) in the network. Any station in the network, including slave stations may send and receive messages that may be addressed to one or more of the other stations. The master station sends commands to the slave stations and keeps track of their status. For example, a master station in New York can control and monitor the status of a remote, unmanned cite in West Virginia by sending commands, such as directions to perform a function, and periodic requests for information (e.g., operating capability of each piece of equipment, communications backlog, unauthorized entry into the facility, etc.) The master station may use any appropriate communication medium to communicate with the slave stations, including radio, land lines, local or wide area network connections, etc. Each station may include appropriate computer equipment (e.g., processor, modem, etc.) to be able to function in the network, and appropriate transmission and reception equipment for the data, video, telephone signals, and the commands. Typically, upon receiving a command, a station will send a responsive message to the sender.
Such systems have several disadvantages. For example, when the master station requests status information, and such information has been provided by the slave station, the slave station clears the reported information (known as "latched" or "time stamped" information). Thereafter, any other station sending a status inquiry would not receive the previous information and receives the current status (known as "on the fly" information) (after all, from the slave station's point of view, the information has been provided to the only station that needs to know the information). Further, even if a slave station were to monitor the network, it probably would not hear the questions and answers together and would thus be unable to determine the status of other stations. For example, a slave station responding to a request for the status of an antenna coupler may reply simply, "up" or "down". Without knowing the question, a listener would be unable to learn anything from the transmission.
Further, while such systems may adequately support the functions at the master station, they do not provide flexibility so that the functions of the master station may be performed at a slave station. For example, a maintenance worker at a slave station may need to know how a particular action he is taking affects the remainder of the network, but cannot unless he establishes a separate communications link with the master station that, at best, would be able to provide a delayed indication of network reaction.
As is apparent, the master station plays an important role in operating the network and various back-up systems for the master station have been devised. For example, one of the slave stations may be configured to assume the duties of the master station, should the master station fail. While this system may present a cost effective procurement option, the system is not likely to be able to bring the slave station on line as a master station quickly enough to prevent gaps in control and loss of data.
A more costly approach is to provide tandem master stations, both being on line and operating as masters. However, neither is aware of the actions of the other and most master station commands are duplicated. For example, a network having master stations at New York and Chicago would send duplicate status inquiries to a West Virginia slave station. In addition, such systems are difficult to set up and maintain because of synchronization (connection and protocol) problems inherent with two master stations.
Existing supervisory systems that include more than one master station also do not afford much flexibility in network design and/or reconfiguration. For example, in prior art systems once the network configuration has been set (including the number of master stations), the number and/or configuration of the master stations cannot later be changed (or changed only with substantial difficulty) to accommodate changed requirements.
By way of example, Badger Technology, Inc. of Milpitas, California manufactures a Dodge 2000.TM. monitoring and control system typical of prior art systems.
The system and method of the present invention may be implemented in existing computer networks that have plural slave stations that receive commands from a master station, such as local or wide area networks. More particularly, and with reference to FIG. 1, the system and method of the present invention may find application in communications networks having plural stations, such as stations N1-N26 shown in FIG. 1. The stations may be arrayed linearly, in a star, or in loops, with any arrangement of interconnections. In an existing communications network in which the present invention may be used, the stations communicate data using microwave radio transmissions. Such networks are well known in the art and need not be described in detail for an understanding of the present invention. See, for example, the network in application Ser. No. 833,233 whose inventorship and ownership is the same as this application, or the network in U.S. Pat. No. 4,319,338 issued Mar. 9, 1982 to Grudowski, et al.
The term communications network, as used herein, refers to an entire network of stations that communicate with each other, or a portion of such a network (e.g., one of the loops L1-L3 of FIG. 1), that is under the control of the supervisory system of the present invention.
Accordingly, it is an object of the present invention to provide a novel system and method for supervising a communications network with multiple masters that obviates the problems of the prior art.
It is a further object of the present invention to provide a novel system and method for supervising a communications network in which any number of master stations may independently attempt to exercise control over the slave stations at any time.
It is still a further object of the present invention to provide a novel system and method for supervising a communications network in which multiple master stations actively and continuously monitor the communications between stations in the network.
It is yet a further object of the present invention to provide a novel system and method for supervising a communication network in which commands from multiple master stations are identified in command-responsive signals from the slave stations so that master stations are aware of the status of the slave stations.
It is another object of the present invention to provide a novel communications network with multiple master stations in which each master station monitors the status of all of the slave stations and attempts to act as the master of the entire network.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.